This invention relates to abrasive tools suited for use in lapping, polishing, texturing, and various other finishes of precision machine parts, e.g., hard disks, magnetic heads, ceramics, plastics, and jewels. The tools of the invention prove particularly effective in texturing and lapping hard disks and flexible disks.
Abrasive tools of the prior art typically comprise a base of polyethylene terephthalate (PET) film, disk, sheet, or the like and a coating material consisting of an abrasive powder dispersed in a binder resin and applied to the base to form a continuous or discontinuous abrasive layer thereon. The abrasive employed is the powder of diamond, alumina, silicon carbide, iron oxide, chromium oxide, or the like.
High precision grinding requires an abrasive powder of uniform particle size distribution. However, the smaller the particle diameter of the abrasive, the greater the difficulties involved in uniformly dispersing the abrasive in the resin because of an increasing tendency toward particle agglomeration. The abrasive particles, when applied in the agglomerated state, can scratch the workpiece or produce an ununiformly ground surface on the workpiece, resulting in uneven grinding. Especially, the surface texturing of magnetic hard disks calls for grinding to uniform width and depth. Conventionally manufactured abrasive tapes for hard disks have an abrasive coat of multilayer structure, with the particles densely in contact with one another and constituting a uniform surface structure, or Benard cell structure. Microscopically, however, the surface in no way uniform; at multitudinous points agglomerated abrasive particles form larger grains which protrude from the abrasive coat surface to produce deep flaws or scratches on the workpiece.
The uniformity of abrasive surface of an abrasive film is of key importance for a grinding system where the surface structure configurations of the abrasive tape are directly transferred onto the workpiece as the ground surface, as is the case with the texturing of a hard disk. Unfortunately, with conventional abrasive films of multilayer, Benard cell structure, surface uniformity is seldom attained.
In the grinding of such other workpieces as magnetic heads, agglomerated grains of abrasive again scratch or otherwise damage them. Moreover, dense formation of the grains on the abrasive layer surface provides an enlarged area of contact between the abrasive layer and the workpiece, with a corresponding increase in the friction with the workpiece. This is turn causes fusing of the binder resin and hampers the removal of grinding dust, both leading to loading and shortened abrasive film life.